One shot operation circuit for a gas discharge lamp



Feb. 24, 1970 v A. MATHISEN I 3,497,768

ONE SHOT OPERATION CIRCUIT F 'Q R A GAS DLSCHARGE LAMP Filed Match 5.1968 gan INVENTOR.

United States Patent 3,497,768 ONE SHOT OPERATION CIRCUIT FOR A GASDISCHARGE LAMP Henry A. Mathisen, Northhrook, Ill., assignor toAddressograph-Multigraph Corporation, Mount Prospect, 11]., acorporation of Delaware Filed Mar. 5, 1968, Ser. No. 710,482 Int. Cl.H05!) 41/00, 41/36, 41/14 US. Cl. 315183 6 Claims ABSTRACT OF THEDISCLOSURE A control circuit to flash a xenon lamp includes a siliconcontrolled rectifier (SCR) that is placed in conduction by a one-shottrigger circuit to connect the lamp across an alternating currentpotential source for a single half cycle. A normally charged capacitoris discharged through a pulse transformer and the conductive SCR topulse the starter electrode of the lamp in synchronism with theconnection of the lamp to the potential supply.

This invention relates to electrical controls for a high intensityradiation source, and more particularly, to a control for controllingthe short duration energization of a high intensity radiation source orlamp using an alternating current supply.

The high intensity radiation sources or lamps with which this inventioncan be used are usually of the gas filled type, such as xenon, and areparticularly useful in photo imaging processes, although they can beused in other applications where high intensity radiation is requiredover a very short time span. Electrical control systems heretofore knownfor energizing a high intensity radiation source for a short duration oftime relied upon one or a bank of capacitors to provide the source ofenergy to energize the radiation source. The use of such a controlsystem was costly, required a great deal of space, and from thestandpoint of safety did not lend itself for use in equipment to beoperated by untrained personnel. Hence, they were not suitable forincorporation into equipment designated for general oflice use.

It is a general object of this invention to provide an improvedelectrical control for energizing a high intensity radiation source thatis compact, economical, and simple to operate.

It is an object of this invention to provide an improved electricalcontrol for energizing a high intensity radiation source for a shortduration that is powered by an alternating current potential source.

It is another object of this invention to provide a high intensityradiation source that can be energized for very short periods of timefor use in conjunction with a photo exposure system.

Another object is to provide a control circuit for connecting a highintensity lamp with an alternating current potential source, whichcircuit includes means for synchronizing the energization of a starterelectrode for the lamp with the connection of the lamp to the potentialsource.

In accordance with these and many other objects, an embodiment of thepresent invention comprises a circuit for controlling the energizationof a high intensity radiation source or lamp which uses an alternatingcurrent po ential source and which does not requi e one or more ratherlarge storage capacitors. This circuit is such that the energization ofa starter electrode on the lamp is svnch onized with the connection ofthe lamp to the alt rnating current potential source. More specifically,the cont ol circuit includes a controlled conduction device or siliconcontrolled rectifier connected in series with the two main terminals ofa xenon lamp across the output 3,497,768 Patented Feb. 24, 1970 ICCterminals of an alternating current potential source. To provide meansfor pulsing the starter electrode of the lamp, a capacitor normallycharged from the potential source is coupled to one winding of a pulsetransformer, the other winding of which is coupled to the starterelectrode. When the lamp is to be energized, a trigger circuit placesthe silicon controlled rectifier in a conductive state to connect themain terminals of the lamp directly across the alternating currentpotential source during a properly poled half cycle of the inputpotential, and the storage capacitor also discharges through theconductive silicon controlled rectifier and the connected winding of thepulse transformer to apply an ionizing or starting potential to thestarter electrode of the lamp. Thus the lamp is energized forapproximately one-half cycle of the alternating current input potentialto provide a short duration, high intensity source of radiation. Thetriggering circuit can be actuated manually or in synchronism with themovement of the web or sheet material through the copying machine.

Many other objects and advantages of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawings in which-- FIG. 1 forms a schematiccircuit diagram of a control circuit embodying the present invention;and

FIG. 2 illustrates a modified form of the circuit shown in FIG. 1.

Referring now more specifically to FIG. 1 of the draw ings, therein isillustrated a control circuit which embodies the present invention andwhich is indicated generally as 10. The control circuit 10 providesmeans for effecting controlled short duration energization of a highintensity radiation source such as a xenon lamp 12 from a conventionalalternating current potential source and without requiring the use ofstorage capacitors of substantial value. The lamp 12 is of conventionalconstruction and includes a pair of main electrodes 14 and 16 and astarter or auxiliary electrode 18.

The circuit 10 is energized from a conventional sixty cycle, voltalternating current source which is connected to primary winding 20A ofa step-up transformer 20, the secondary winding 20B of which provides anoutput potential on the order of 500 volts. The lamp 12 is adapted to beconnected directly in series across the secondary 'winding 20B over acircuit including a rectifier or unidirectional conducting device 22, asilicon controlled rectifier or controlled conduction device 24, andanother unidirectional conducting device or rectifier 26. The controlledconduction device includes two output electrodes, i.e., the cathode andanode, and a control or gate electrode. The silicon controlled rectifier24 is normally in a nonconductive state and, when triggered to aconductive state, connects the lamp 12 directly across the alternatingcurrent potential source to be energized during a selected positivelypoled half cycle of the input potential.

In the normal condition of the circuit 10, a small storage capacitor 28is charged through the rectifier 22 and a resistance element 30 duringthe positively poled half cycles of the input potential. The capacitor28 is also connected to the anode of the silicon controlled rectifier 24through a resistance element 32 which is shunted across the two mainterminals 14 and 16 of the lamp 12. Thus, after the capacitor 28 ischarged, a positive potential is applied to the anode of the siliconcontrolled rectifier 28 during both the positive and negative halfcycles of the alternating current potential supply.

A one-shot trigger circuit indicated generally as 34 provides a meansfor energizing the lamp 12 during a single positive-going half cycle ofthe alternating current input potential. The trigger circuit 34 includesa switch 36 providing a pair of normally closed contacts 36A and a pairof normally open contacts 36B. The switch 36 can be manually operated orin photocopying machines, may be operated under the control of sheet orweb material. In the normal position of the switch 36, the closedcontacts 36A provide a circuit for discharging a capacitor 38 through aseries connected resistance 40. The normally open contacts 36B of theswitch 36 are connected to the cathode of the silicon controlledrectifier 24, the gate electrode of which is returned to one side of thesecondary winding 20B through a resistance element 42.

When the control circuit is to be actuated to flash or energize the lamp12, the switch 36 is operated to open the contacts 36A and to close thecontacts 363. The closure of the contacts 36B does not have any effecton the circuit 10 during the positive-going half cycles. However, on thefirst negative-going half cycle occurring following the closure of thecontacts 36B, a circuit is completed for charging the capacitor 38extending from one side of the secondary winding B through a diode 44,the resistance element 40, the capacitor 38, the closed contacts 36B,the control gap between the cathode and gate electrodes of the siliconcontrolled rectifier 24, the resistance element 42 to the other terminalof the secondary winding 20B. The current flowing over this path tocharge the capacitor 38 biases the control gap betwen the gate electrodeand the cathode of the silicon controlled rectifier 24 to trigger thisrectifier into a conductive condition. Since the upper terminal of thesecondary winding 20B is negative with respect to the lower terminal atthe time that bias current is applied to the rectifier 24, the diode 22is reverse biased, and the capacitor 28 provides the holding current forthe rectified 24 by discharging through the resistance elements 30 and32 and the diode 26. The values of the resistance elements 30 and 32 andthe capacitor 28 are so chosen that the capacitor 28 will be dischargedto the point at which holding current for the rectifier 24 can besustained for no longer than one half cycle.

On the following positive-going half cycle, conduction through therectifier 24 is sustained by the potential supplied by the secondarywinding 20B, and the main electrodes 14 and 16 of the lamp 12 areconnected directly across this secondary winding through the forwardbiased diodes 22 and 26 and the conductive rectifier 24. The lamp 12,however, is not placed in a conductive or ionized condition until astarting or ionizing pulse is applied to the auxiliary or starterelectrode 18, and this start signal is applied by a starter controlcircuit indicated generally as 46.

In the normal condition of the circuit 10, a relatively low valuestorage capacitor 48 is charged to a positive potential by the inputalternating current supply potential over a circuit including a diode orrectifier 50 and a series connected resistance element 52. The capacitor48 is connected in parallel with the silicon controlled rectifier 24 andthe rectifier or diode 26 over a circuit including a diode or rectifier54 and a primary winding 56A of a pulse transformer 56. The secondarywinding 56B of the pulse transformer 56 is connected to the starterelectrode 18.

When the silicon controlled rectifier 24 is placed in a conductivestate, the capacitor 48 discharges through the primary winding 56A, thediode or rectifier 54, the silicon controlled rectifier 24, and thediode or rectifier 26 so that a pulse of substantial magnitude, e.g., onthe order of 15 kv., is coupled by the secondary winding 56B to thestarter electrode 18. The application of this relatively high potentialpulse to the starter electrode 18 ionizes the gas, such as xenon, in thelamp 12 and thus flashes the lamp 12 during the positive-going halfcycle next following the negative-going half cycle in which the switch36 was closed. At the end of this half cycle, the lamp 12 is returned toits normal state independent of the operated or released condition ofthe control switch 36.

More specifically, even though the switch 36 is maintained in anoperated state so that the contacts 36B are closed following thepositive half cycle during which the lamp 12 was flashed, the reversalin polarity of the alternating current supply potential removes theholding current from the silicon controlled rectifier 24, the capacitors28 and 48 having been discharged, and the rectifier 24 returns to anonconductive state. Even though the contacts 36B are held in a closedcondition, the time con- 'stants for the charging circuit for thecapacitor 38 are so chosen that the capacitor 38 is now fully charged toblock current to the gate electrode, and thus the control gap betweenthe cathode and gate electrodes of the rectifier 24 cannot be biasedthereafter until the switch 36 has been released to open the contacts36B and to close the contacts 36A. When the contacts 36A are closed, thecapacitor 38 discharges through the resistance element 40.

During the interval following the flashing of the lamp 12, thecapacitors 28 and 48 are charged on positive-going half cycles and thecontrol circuit 10 is restored to a normal condition. These capacitorsprovide only control potentials for the circuit 10, and the current foroperating the lamp or radiation source 12 is supplied directly from thealternating current input potential.

FIG. 2 of the drawings illustrates a modified form of the circuit 10 inwhich the lamp 12 includes the main electrodes 14 and 18 and thesecondary winding 56B of the pulse transformer 56 is connected to theelectrode 14. When the rectifier 24 is placed in a conductive condition,the pulse developed in the winding 56B is applied across the electrodes14 and 16 to trigger the lamp into a conductive state. The operation ofthe circuit 10 connected in the manner shown in FIG. 2 is in otherrespects similar to the operation of the circuit shown in FIG. 1.

Although the control circuit 10 can be made using component values inranges suitable for each particular application, as is well known tothose in the art, the following table lists component values for onecontrol circuit 10 made in accordance with the present invention:

TABLE Capacitor 28 ,u.fCl 10 Resistance element 30 ohms 330 Resistanceelement 32 do 87 Capacitor 38 ufd .1 Resistance element 40 ohmsResistance element 42 do 100 Capacitor 48 Mfd .5 Resistance element 52ohms K Although the present invention has been described with referenceto two illustrative embodiments thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art that Will fall Within the spirit and scope of theprinciples of this invention.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. A control circuit for use with a potential source comprising:

a gaseous discharge lamp provided with electrode means,

a controlled conduction device including a pair of output electrodes anda control electrode,

first circuit means connecting the electrode means of the lamp and thetwo output electrodes of the device in series across the potentialsource,

a trigger circuit connected between the potential source and device forapplying a bias between the control electrode and one of the outputelectrodes for placing the device in a conductive state for apredetermined interval, said trigger circuit including bias blockingmeans for blocking the application of a bias between the controlelectrode and said one output electrode subsequent to said predeterminedinterval, thereby to limit the conduction of said controlled conductiondevice, and

second circuit means connected between one of the output electrodes ofthe device and the electrode means for energizing the electrode means inresponse to conduction through the device.

2. A control circuit for use with an alternating current potentialsource comprising a lamp including two main electrodes and a starterelectrode,

a controlled conduction rectifier having two output electrodes and agate electrode,

first circuit means connecting the two main electrodes of the lamp andthe two output electrodes of the rectifier in series across thealternating current potential source,

a trigger circuit connected between the potential source and therectifier to apply a bias between the gate electrode and one of theoutput electrodes for placing the rectifier in a conductive state toconnect the main terminal of the lamp to the alternating currentpotential source,

capacitor means,

second circuit means including a unidirectional conducting device forconnecting the capacitive means to the potential source for charging thecapacitive means,

and third circuit means coupled to the starter electrode for applying astart signal to the starter electrode, said third circuit meansincluding means for discharging the capacitive means through theconductive rectifier.

3. A control circuit for energizing a load from an alternating currentpotential source comprising a gas-filled lamp having a pair of mainelectrodes and a starter electrode,

a silicon controlled rectifier having a pair of output electrodes and agate electrode,

first circuit means connecting the two main electrodes of the lamp andthe two output electrodes of the rectifier in series across thealternating current potential source,

a trigger circuit connected between the potential source and rectifierto apply a bias between one of the main electrodes and the gateelectrode for placing the rectifier in a conductive condition to connectthe main terminals of the lamp to the potential source,

a pulse transformer having first and second windings,

second circuit means connecting the first winding of the transformer tothe starter electrode,

capactive means charged from the potential source, and third circuitmeans connecting the capacitive means and the second winding of thepulse transformer across the rectifier so that the capacitive means discharges through the rectifier and the second winding when the rectifieris placed in a conductive condition so as to place a signal on thestarter electrode.

4. The control circuit set forth in claim 3 in which the trigger circuitincludes a capacitor and switch means for controlling the connection ofthe capacitor to the rectifier.

5. The control circuit set forth in claim 3 in which the first circuitmeans includes a unidirectional conducting device poled in the samedirection as the rectifier, and in which a storage capacitor isconnected in series with the unidirectional device and in parallel withthe lamp and rectifier.

6, A control circuit for controlling the energization of a triggeredload by an alternating current potential source comprising a lamp havinga pair of main electrodes and a starter electrode,

a normally non-conductive controlled conduction device having a pair ofoutput electrodes,

first circuit means connecting the two main electrodes of the lamp andthe two output electrodes of the device in series with the alternatingpotential source,

a trigger circuit connected to the device and operable to place thedevice in a conductive condition to connect the lamp to the alternatingcurrent potential source, and

a synchronizing circuit connected between the starter electrode of thelamp and the device and responsive to conduction through the device forapplying an energizing signal to the starter electrode.

References Cited UNITED STATES PATENTS 3,278,799 10/1966 Gordy 3l5--1713,416,031 12/1968 Franks et al. 3l5119 JAMES W. LAWRENCE, PrimaryExaminer C. R. CAMPBELL, Assistant Examiner US. Cl. X.R.

